THE UPPER TRIASSIC OF WESTERN TEXAS. 31 



pit in the basisphenoid. The suture between it and the basisphenoid is not distinct, 

 but on either side of the pit there is a deep groove which marks the position of the- 

 suture; it is possible that the sutural region was occupied in life by a considerable mass 

 of cartilage, which in its decay has left the groove. The upper part of the anterior 

 edge is marked by a sharp, thin ridge; just anterior to this is a large foramen through 

 which passed the jugular vein and the IX, X, and XI nerves. Near the posterior edge 

 there are small foramina in the exoccipital portion of the complex, which permitted 

 the escape of the XII nerves. 



The basisphenoid.- The lower surface is marked by the presence of a remarkably 

 large and deep conical pit. This is in the position of the openings of the Eustachian 

 canals in the Crocodilia, but the pit was thoroughly cleaned out and no traces of such 

 openings could be detected. On either side of the pit the bone is thickened and passes 

 forward to form the prominent basipterygoid processes. Posterior to the processes 

 the sides of the bone are marked by a groove and then swell backward and outward 

 to the edge of the groove which marks the line between the basisphenoid and the 

 basioccipital. Between the basipterygoid processes there is a thin parasphenoid rostrum 

 of considerable vertical extent. The anterior portion has been injured by decay, but 

 it is apparent that not a great deal has been lost. The upper part of the posterior end 

 of this process is excavated to receive the lower end of the infundibulum and the edges 

 of this excavation are continuous with the alisphenoids above. The anterior face of 

 the basisphenoid is rather broad and slightly inclined backward to the posterior face 

 of the cavity for the infundibulum. Near the middle of this face there is a pair of 

 foramina for the entrance of the internal carotid arteries. The point of juncture of 

 the basisphenoid and the bones above is not determinable. From the bottom of the 

 pit on the upper surface of the posterior portion of the parasphenoid rostrum foramina 

 run through the sides of the basisphenoid to open into the lower part of the groove 

 described as lying posterior to the basipterygoid processes; the function of these foramina 

 is not known. 



The walls of the brain-case (fig. 7 E) are formed by the alisphenoids, the prootics, 

 the epiotics (?), and the opisthotics, which form a solid lateral mass without distinguish- 

 ing sutures. The outer surface of the brain-case is marked by two distinct ridges. 

 The first starts below the origin of the bar between the orbit and the temporal opening 

 and descends almost vertically, becoming continuous with the anterior edge of the 

 alisphenoid at a point about one-third of its height above its origin from the parasphenoid 

 rostrum. This ridge probably marks the line of contact between the prootic and the 

 alisphenoid. 



The lower ends of the alisphenoids are closely approximated, forming a narrow 

 opening through which the hypophysis extends into the infundibular cavity below; 

 above this the anterior edges of the bones rise nearly vertically, with a slight notch 

 which permitted the escape of the III and IV nerves; at about one-half of their height 

 the edges incline gently forward and contract into a second notch which marks the 

 escape of the II pair of nerves; beyond this they incline more sharply forward and 

 diverge to their contact with the upper wall of the skull. 



Posterior to the first ridge, the walls of the brain-case are concave and perforated 

 by the large foramina for the V nerves; the bulk of this portion of the wall is formed by 

 the prootic. The second, or posterior, ridge on the wall of the brain-case comes sharply 

 forward from the rear. Its posterior portion is formed by the lower edge of the opisthotic; 

 just above the otic opening it bends sharply downward and forward and very nearly 

 reaches the lower end of the first ridge. There are no sutures visible in the space between 

 these ridges, but there is a short, low elevation extending forward from just below the 



